1. Field of the Invention
This invention relates to a liquid supply apparatus, and in particular to improvements in a liquid replenishing mechanism.
2. Description of the Prior Art
Some conventional liquid supply apparatuses, for example, apparatuses for supplying ink to recording means in recording apparatuses, are designed such that the supply of ink to the ink reservoir unit thereof is effected by a cartridge type ink supply tank so that the liquid level of the ink in the ink reservoir unit can be maintained constant and the ink supply pressure always becomes constant.
In such apparatuses, the supply tank itself is adapted to be interchanged if the ink to be supplied therein is exhausted. With such ink supply apparatuses, it has often been the case that when the ink supply tank is interchanged, the operator's hands are stained by ink or the instruments around the tank are stained by ink, and the ink supply tank has been inconvenient to handle.
As a kind of the aforementioned recording apparatus, there has been proposed an on-demand type ink jet printer in which drops of ink are discharged from a nozzle by a pressurization pulse to thereby effect recording. In such a printer, when the pressurization pulse is not applied, ink must not be discharged from the nozzle although, ink must be quickly discharged in response to a pressurization pulse. Therefore it is not suitable to pressurize the ink as by a pump and supply it to the nozzle and the ink is supplied chiefly by utilization of capillary phenomenon. Therefore, when the liquid chamber of the nozzle becomes empty during apparatus assembling work or maintenance and adjustment work, directing the ink in the ink tank to the nozzle and filling the nozzle with the ink is required.
For this reason, in some apparatuses, a pumping mechanism is provided in the ink passage from the ink tank to the nozzle of the head to effect fill the nozzle. In such apparatuses, a check valve is usually provided to prevent backflow of the ink in the ink passage when the ink is pressurized by the pump.
However, a good checking characteristic and a small resistance in a forward direction are generally required of the check valve used in such apparatuses. However, the check valve generally has a good checking characteristic, but its resistance in the forward direction of the liquid supply path in the on-demand type printer is too great and thus, it has been difficult to construct a proper liquid supply mechanism.